Speaking of elision though, I don't quite understand how you can elide something and still keep the meter. In this case, the extra 'o' was removed so the meter would be kept, but I think elision happens a lot on an already conformant line. Can somebody elucidate this for me?

No, elision is a feature of the language that is capitalized on in poetry to force meters to work. If a line had to scan even without elision, then Vergil would have to have been drunk when he wrote litora multum ille et terris iactatus et alto.